The present application is based on Japanese Patent Application No. 11-141479 filed May 21, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to an optical water-absorptive gel and an ophthalmic material formed of the optical water-absorptive gel. In particular, the invention is concerned with the optical water-absorptive gel in which fine particles of a metal oxide are dispersed and which is capable of absorbing ultraviolet (UV) rays, and the ophthalmic material for a contact lens, an intraocular lens, an artificial cornea, etc.
2. Discussion of the Related Art
Water-absorptive gels (hydrogels) which are water-swollen with water held therein have been conventionally used for various applications. In the field of an ophthalmic material, for instance, a lens material for a contact lens or an intraocular lens, and an artificial cornea are advantageously formed of the water-absorptive gels, while utilizing characteristics of the water-absorptive gels.
An intraocular lens which is implanted in a patient""s eye from which a crystalline lens has been removed in a cataract surgery, and a contact lens which is worn on a wearer""s eye for rectifying the wearer""s eyesight are preferably formed of a material capable of substantially preventing transmission therethrough of ultraviolet (UV) rays, like a natural crystalline of a human eye. In view of this, the lens material is generally formed of a water-absorptive gel to which a suitable UV absorbing agent such as benzotriazoles, benzophenones or derivatives of salicylic acid is added.
Metal oxides are used for various applications. In the field of the above-described lens material, for instance, titanium dioxide is used as a coloring material for producing a colored contact lens as disclosed in JP-A-3-54519. Described more specifically, the publication discloses a method of producing a colored contact lens by dispersing titanium dioxide as a coloring material in a suitable carrier, applying the obtained dispersed product or dispersion to a desired portion of a mold so as to imprint thereon a suitable pattern corresponding to an iris section of an intended lens, and polymerizing a monomer liquid introduced into the mold. The contact lens obtained according to the disclosed method has a colored iris section corresponding to the pattern imprinted on the above-indicated portion of the mold. JP-A-6-347782 and JP-A-8-152582 also disclose a method of producing a colored contact lens by first applying a coating of an ink including a coloring material such as iron oxide, chromium oxide or titanium oxide, to a surface portion of a base contact lens corresponding to its iris section, and then curing the ink, so that a colored layer which gives a colored iris section is formed on the above-indicated surface portion of the lens. All of the techniques disclosed in the above-indicated publications are intended to form the colored iris section in the contact lens, in other words, the obtained lens is used as an artificial eye or ocular prosthesis, wherein the colored iris section is opaque.
As a result of an extensive study about the water-absorptive gels made by the inventors of the present invention, the inventors have found a water-absorptive gel having a high degree of transparency sufficient for an optical use and capable of maintaining a desired shape, wherein a predetermined cross-linked water-absorptive polymer is swollen in an aqueous medium in which fine particles of a metal oxide are finely dispersed. In addition, it has been found that such water-absorptive gel can be advantageously used as an ophthalmic material exhibiting an excellent ultraviolet-ray-absorbing property.
It is therefore an object of the present invention to provide a novel optical water-absorptive gel exhibiting excellent characteristics. It is also an object of the invention to provide an ultraviolet-ray-absorbing ophthalmic material for a lens material or an artificial cornea, using the water-absorptive gel.
The objects of the present invention may be attained according to a principle of the invention, which provides an optical water-absorptive gel having a predetermined shape and consisting of a cross-linked water-absorptive polymer and an aqueous medium in which fine particles of a metal oxide are finely dispersed, the cross-linked water-absorptive polymer being swollen in the aqueous medium, so as to provide the predetermined shape in a gel state.
In the present optical water-absorptive gel, in spite of the inclusion of the metal oxide, the water-absorptive gel exhibits excellent optical characteristics having a sufficiently high degree of transparency, since the metal oxide is dispersed in the water-absorptive gel in the form of fine particles. The present water-absorptive gel wherein the fine particles of the metal oxide are dispersed exhibits excellent UV-ray-absorbing characteristics, so that the present water-absorptive gel can be advantageously used as an ophthalmic material such as a lens material for a contact lens or an intraocular lens, and an artificial cornea.
In a first preferred form of the present invention, the cross-linked water-absorptive polymer is formed by polymerizing at least one hydrophilic monomer and at least one cross-linkable monomer in the aqueous medium in which the fine particles of the metal oxide are finely dispersed. In the optical water-absorptive gel according to this arrangement, the predetermined cross-linked water-absorptive polymer is swollen in the aqueous medium such that the fine particles of the metal oxide are dispersed in the swollen polymer. The thus constructed water-absorptive gel has a predetermined shape.
In a second preferred form of the present invention, the fine particles of the metal oxide have a diameter of not greater than 25 nm. This arrangement permits the water-absorptive gel to have a sufficiently high degree of transparency.
In a third preferred form of the present invention, the metal oxide is selected from the group consisting of zinc oxide and titanium oxide.
In a fourth preferred form of the present invention, the metal oxide is dispersed in the aqueous medium in an amount of 0.3-5 wt.% of the cross-linked water-absorptive polymer. According to this arrangement, the water-absorptive gel exhibits excellent UV-ray-absorbing characteristics as well as a high degree of transparency.
In a fifth preferred form of the present invention, a ratio of the cross-linked water-absorptive polymer and the aqueous medium on a weight basis is held within a range of 90:10xcx9c20:80
In a sixth preferred form of the present invention, the at least one hydrophilic monomer is selected from the group consisting of hydroxyl group-containing (meth)acrylates, (meth)acrylamides and derivatives thereof, vinyl lactams, and (meth)acrylic acid.
The above-indicated objects of the present invention may also be attained according to another aspect of the present invention, which provides an ophthalmic material formed of the optical water-absorptive gel according to the above-described aspect of the invention, the optical water-absorptive gel absorbing UV rays. According to this arrangement, the optical water-absorptive gel is advantageously used as the ophthalmic material by making maximum use of the characteristics of the gel. The ophthalmic material comprises a lens material for a contact lens or an intraocular lens, and an artificial cornea.